One of the more common techniques employed for the polymerization of olefins involves carrying the polymerization out in a liquid diluent under conditions such that the polymer is formed in the forms of solid particles such that the reaction product is a slurry of particulate polymer solids suspended in a liquid medium. Such reaction techniques have been referred to as slurry or particle form polymerizations. A particularly desirable method for carrying out such particle form polymerization involves the use of continuous loop-type reactors. Examples of such reactor systems are disclosed in U.S. Pat. No. 3,152,872 and U.S. Pat. No. 4,424,341, the disclosures of which are incorporated herein by reference.
In the past, many of the commercial particle form polymerization processes have used chromium based catalysts. Such processes have, however, also been carried out using titanium based catalyst and organometallic cocatalysts.
When using low levels of cocatalyst in the particle form polymerization the applicants have noted some problems in using a titanium based catalyst. Even though the levels of cocatalysts are high enough to ensure sufficient productivity, it has been observed that with a titanium-containing catalyst system when the level of cocatalyst drops below a certain level there is a tendency for a skin of some type to form within the reactor walls inhibiting heat transfer. On bench scale units where the polymerization is only an hour or so long and where heat transfer is usually not critical the phenomena is usually not observed. However, in commercial scale polymerizations, particularly in loop reactors the phenomena has been observed.
The exact nature of this skin formation is not understood at this time. It has been theorized by the applicants that it may be due to the formation of soluble polymer or soluble catalyst. One theory of the applicants is that it may actually be due to the bleeding off of hydrocarbon soluble species from the catalyst.
An object of the present invention is to provide a method for the particle form polymerization of olefins using a titanium containing catalyst system with a reduced tendency to cause the formation of a skin during the polymerization.
Another object of the present invention is to provide a process for the particle form polymerization of olefins using a titanium based catalyst which can be employed satisfactorily with low cocatalyst levels.
Another object of the present invention is to provide a titanium catalyst which can be used in a commercial scale particle form polymerization without the employment of high levels of cocatalyst.
Other aspects, objects, and advantages of the present invention will be apparent to those skilled in the art having the benefit of the following disclosure.